Infrared polarimetry is a technique for acquiring and processing emissive and scattered radiation in the infrared bands and, as such, has applications in astronomy, space exploration, materials characterization, plasma diagnostics, biological measurements and characterization of military targets. In the military, exemplar applications of polarization information occur in enhancement of the discrimination of targets from clutter and enhancement of feature identification. These enhancements reduce false alarm rates in both human and automatic target recognition and enable improvements in target classification, counter-measure rejection and defeat of camouflage.
However, infrared polarimetry is still in a rather immature state of development. Hence it is not used in any existing or planned military system, even though some research has indicated that infrared polarization imagery can provide surface orientation information, distinction between flat plates and cylinders and discrimination between tanks and heated flat plate decoys, all based on differences in polarization signatures of the various items. It has been discovered further that polarization imagery is possible with relatively cool objects.
Much of the difficulties encountered both in military and peaceful applications of the nascent infrared polarimetry are due to significant limitations in the extant instrumentation. One such limitation is the polarization aberrations introduced by the instrument itself. In addition, optical components of the instruments introduce some change in the polarization state of the infrared radiation as the radiation propagates through the instrument. Optical coatings, scattering and birefringence effects also may cause unintended changes in the polarization state that perturb the intended polarization changes wrought about by the polarizers and retarders.